1. Field of the Invention
The present invention relates to a PBN container in which a conductive film is laminated on a surface of a body formed by depositing PBN (pyrolytic boron nitride), and relates to a method for producing the PBN container.
2. Description of the Related Art
PBN is manufactured by using a pyrolysis method. Therefore, PBN has a kind of laminar film structure in a microscopical view. And, PBN has anisotropy between a surface direction and a thickness direction of the laminar film. Such PBN has various advantages that a container of high purity can be easily formed by CVD method, and contamination derived from the container can be prevented, and so on. Therefore, PBN has been used as material of various containers such as a hearth liner for electron beam evaporation, a container for MBE (molecular beam epitaxy), a container for metal melting, and a container for analysis.
Here, a hearth liner for electron beam evaporation is quoted as an example of a PBN container and is described below.
Electron beam evaporation is a useful method for forming a thin film on a substrate. In electron beam evaporation, electron beam is irradiated into evaporation material, thereby to heat and evaporate the material, and the evaporated material is deposited onto the substrate, and thus, a thin film is formed on the substrate (see, for example, “Handbook of Thin Film Engineering”, published by Ohm Company, p 101-p 105, published on Dec. 10, 1983 (Showa 58)). For example, a hearth liner for electron beam evaporation is put in a water-cooled copper crucible (hearth), electron beam is irradiated into evaporation material filled in the hearth liner by an electron gun, and thereby the evaporation material is evaporated.
In this case, the evaporation material can be also directly filled in a hearth without using the hearth liner for electron beam evaporation. However, a hearth liner can be brought out to clean, and so cleaning is easy. And, when it is desired that a evaporation material is deposit onto a substrate, hearth liners may be merely exchanged, and so the operation is simple, and also contamination can be prevented. Therefore, a hearth liner for electron beam evaporation is generally used.
FIG. 5 is a schematic sectional view illustrating one example of a hearth liner for electron beam evaporation and a hearth. The hearth liner 50 for electron beam evaporation is put in a copper hearth 51, and the bottom contacts with the hearth 51. The hearth 51 is cooled by cooling water 52. Moreover, evaporation material 53 such as aluminum is filled in the hearth liner 50 as shown in the figure.
As such a hearth liner for electron beam evaporation, it is also known that it is made of carbon as well as PBN. However, there is a problem that the hearth liner made of carbon can react with the evaporation material. For example, if electron beam evaporation is performed by filling aluminum in the hearth liner made of carbon, carbon and aluminum react to generate aluminum carbide (Al4C3). Therefore, a thin film of aluminum deposited onto a substrate is degraded in crystallinity and purity.
To the contrary, the hearth liner made of PBN has an advantage that it is hard to react with an evaporation material. However, even if the hearth liner made of PBN is used, there is a problem as follows. Firstly, an evaporation material can be merely partially melted in the extreme vicinity where electron beam is irradiated, and it is impossible to melt the evaporation material wholly. Moreover, if aluminum is used as an evaporation material, aluminum crawls up along the inner wall surface of the hearth liner by surface tension, and thereby, it is difficult to view a melted state, and a state of the melted spot is bad. Further, because PBN is an insulator, charge-up is caused by irradiating an electron beam. From these reasons, uniform high-purity metal films of large-area could not be stably made.
For solving the problem, a PBN hearth liner in which a conductive film is laminated on a surface of a body formed by depositing PBN has been developed (see, for example, Japanese Patent Application Laid-open (Kokai) No. 09-59766). Because the conductive film is heated by an electron beam in the case of using this PBN hearth liner, an evaporation material can be wholly melted. Further, because there is a conductive film, the problem of charge-up is not caused. Further, it becomes difficult that a melted evaporation material such as aluminum crawls up along the inner wall surface of the hearth liner. Therefore, it was believed that uniform high-purity metal films of large-area could be stably made by using this PBN hearth liner.
However, there was a problem that the PBN hearth liner in which a conductive film is laminated on a surface of a body formed by depositing PBN is easy to break and has a short life. Therefore, a PBN hearth liner excellent in durability has been desired.